This invention relates to a differential locking assembly that utilizes an electronic coil to actuate a differential lock shift collar.
Vehicle drive axles typically include a pair of axle shafts for driving vehicle wheels. The drive axle uses a differential to control input speed and torque to the axle shafts. Under ideal conditions, when the vehicle is driven along a straight path, the wheels will be turning at approximately the same speed and the torque will be equally split between both wheels. When the vehicle negotiates a turn, the outer wheel must travel over a greater distance than the inner wheel. The differential allows the inner wheel to turn at a slower speed than the outer wheel as the vehicle turns.
Power is transmitted from a vehicle drive shaft to a pinion gear that is in constant mesh with a differential ring gear. The ring gear is bolted to a differential housing or case that turns with the ring gear. A differential spider having four (4) support shafts orientated in the shape of a cross, has four (4) differential pinion gears. One pinion gear is supported for rotation on each support shaft. Power is transferred from the differential housing to side gears that are splined to the axle shafts. The side gears are in constant mesh with the side differential pinion gears. The outer ends of the axle shafts are bolted to the brake drum hubs to which the wheels are also bolted.
When the vehicle is driven in a straight path, the ring gear, differential housing, spider, and differential pinion gears all rotate as one unit to transfer power to the axle shafts. There is no relative movement between the differential pinion gears and the side gears. When the vehicle turns, the differential pinion gears rotate on their respective shafts to speed up the rotation of one axle shaft while slowing the rotation of the other axle shaft.
Often the differential includes a differential locking mechanism. When there are poor road conditions, i.e., slippery or rough surfaced roads, the locking mechanism allows maximum wheel and tire traction for improved control. If the differential does not have a locking mechanism and one tire is on ice, all of the torque and speed will be transferred to the wheel on ice. Thus, the tire just spins on the ice and the vehicle is prohibited from traveling forward. A locking mechanism allows the axle shafts to rotate at the same speed while transferring all available torque to the tire not on the ice. If the tractive effort at this tire is sufficient, the vehicle can be moved off of the ice. When the differential is locked, power is transmitted through the locked differential housing, gearing, and axle shafts rather than through the differential gearing only.
One type of differential locking mechanism is comprised of an air actuated shift collar that locks the differential housing to the axle shafts. An air operated shift fork cooperates with the shift collar to engage or disengage the locking mechanism via a driver-controlled switch. In this configuration, one of the axle shafts has two sets of splines. An inner set of splines, closest to the differential, is engaged with one differential side gear, while an outer set of splines cooperates with the shift collar. The shift collar, although engaged with the outer splines at this time, is not engaged with the differential casing, thus the outer splines will rotate at the same speed as this side gear when the main differential is in an unlocked or disengaged position allowing the main differential to operate in a normal manner.
When the driver-controlled switch is activated, air pressure causes a shift linkage to move the shift collar towards the differential. This allows the collar to engage with the differential casing, as well as remaining engaged with the axle shaft outer splines. Power transfer through the differential is now achieved through the locked differential casing, gearing, and both axle shafts together, rather than through the differential gearing alone.
Some disadvantages with the air actuation method are the significant number of components that are required, leakage, and component wear. The significant number of components that are required to operate this system increase assembly time and drive up the overall system cost. Requiring an air connect to actuate the system introduces possible air leaks to the system, which can lead to inadequate system performance. Further, the differential gearing, axle shafts, and shift collar operates in an oil-lubed environment and the additional components for the air actuation method increase the risk of oil leaks in the system. Further, repeated engagements and disengagements between the shift fork and shift collar, especially if engaged at high wheel speeds, can lead to premature component wear as well as introducing premature wear onto related components such as the differential gearing.
Thus, it is desirable to have a simplified actuating mechanism for a differential lock that reduces the overall number of components, operates more efficiently, and is more cost effective, as well as overcoming the other above-mentioned deficiencies with the prior art.